Characteristics of Hot Strip Continuous Mill Production
The hot strip continuous mill process includes descaling, rough rolling, and finishing rolling.
Each stage is similar to medium and thick plate rolling.
However, rough rolling does not widen the slab.
Instead, vertical rolls compress it in the width direction.
During descaling, high-pressure water is used.
Large vertical rolls also press the slab edges.
They apply 50–90 mm of pressure to adjust the width and improve descaling.
Modern mills use isothermal technologies like speed-up rolling, insulation boxes, and coiling boxes.
These change the rolling characteristics, especially in the rough and finishing sections.
Rough rolling
The finishing mill of a modern hot strip mill is mostly composed of 5 to 8 stands, and there is no difference. However, the composition and layout of the rough rolling mill are different depending on the type of hot strip mill, which is characteristic of this mill. We can summarize it as follows:
- A fully continuous hot strip mill uses 5–6 stands for rough rolling.
- A semi-continuous hot strip mill uses either two reversible two-roll mills or one irreversible two-roll mill combined with one reversible four-roll mill. As shown in the figure.
Finishing rolling
The layout of the finishing mill of a hot strip mill is relatively simple, generally consisting of 6-7 four-roll mills.
Selection of mill roll material
1. Recommendation for selection of roll material for large vertical roll (VSB):
VSB is used for descaling and edge rolling. It does not require high surface roughness, but due to the large thermal shock, it requires good thermal fatigue resistance.
Recommended material: alloy cast steel roll with carbon content of 0.7-1.4% and chromium content of 0.8-1.2%.
We recommend Pearlitic Ductile Cast Iron Rolls, which have good thermal stability and mechanical strength and are suitable for VSB working conditions.
2. R1 roughing roll
The two-roll roughing mill has no support rolls. The rolls must withstand high torque and resist thermal cracking. Therefore, they must have high torsion resistance, bending strength and good thermal cracking resistance.
It is recommended to use high chromium composite cast iron rolls or high chromium composite cast steel rolls. Among them, high chromium composite cast steel rolls have the following advantages:
No need for strong water cooling like high chromium composite cast iron.
The thermal conductivity of the working layer of the roll body is better.
In the reversible stand, it can reduce edge wear and improve plate shape.
At the same time, it has good steel bite and thermal crack resistance.
3. Suggestions on the selection of small vertical roll materials:
It is used for edge adjustment of strip billets, and has certain requirements for torsion resistance, bending resistance and wear resistance.
Recommended material: eutectoid alloy cast steel or alloy semi-steel (such as 160CrNiMo).
Optional products: The Pearlitic Ductile Cast Iron Rolls we provide also have excellent toughness and wear resistance, which is suitable for such small vertical roll applications.
4. Suggestions on the selection of materials for finishing mill working rolls:
The continuous finishing mill requires high surface quality and dimensional accuracy. We distinguish the materials because the loads of the front and rear mills are different.
Material configuration recommendations:
Recommended materials for working rolls of finishing mill.
(F1 → F3 (front section)
The reduction is relatively small.
We recommend using high-nickel-chromium infinitely chilled cast iron rolls with a roll body hardness of 70–75 HSD.
F4 → F7 (rear section)
The reduction and heat load are higher.
We recommend using high-nickel-chromium infinitely chilled cast iron rolls with a roll body hardness of 80 HSD.
When the site requires higher red hardness, wear resistance, and dimensional stability, you can select our High-Speed Steel (HSS) Rolls and Hot-Rolled HSS Strip Working Rolls. These rolls perform exceptionally well under high-temperature, high-load continuous rolling in the rear section of finishing stands, significantly extending roll change intervals and improving coil surface quality.
Hot strip mill production has several stages.
Each stage has specific technical demands.
Proper roll material selection is essential.
It ensures high performance under heat and load.
It reduces downtime and saves maintenance costs.
At CYKC, we offer a full range of roll solutions tailored to your mill’s requirements, including pearlitic ductile cast iron rolls, high-chromium composite rolls, and high-speed steel rolls. With advanced metallurgy and precise machining, our rolls help you achieve consistent quality and superior productivity in every ton you roll.
Partner with CYKC GROUP for reliable performance and cost-effective rolling solutions.
E-mail: cykc@cykcgroup.com.cn